Sleep is a highly conserved behavior that is required for proper health and cognition in all animals studied to date, yet a function for sleep has not been described. Drosophila melanogaster exhibits many of the hallmarks of mammalian sleep, including increased arousal threshold, consolidated immobility, and regulation by both circadian rhythm and a homeostatic drive. Although great strides have been made in recent years towards understanding the neural circuitry and molecular pathways that regulate circadian rhythm in Drosophila, the regulation of sleep by the homeostatic drive is poorly understood. In a recent screen for genes involved in regulating sleep behavior, we found that flies lacking a functional copy of the Rab GTPase, lightoid (ltd), sleep at least 200min per 24h less than background controls. In addition, work by others has suggested that (1) the expression of ltd is Clock-dependent, (2) the expression of ltd is sleep/wake-regulated, (3) ltd is required for proper long-term memory, and (4) ltd is a homologue of the human gene, Rab32, which functions to localize PKA, a known regulator of sleep. The goal of the proposed project is to better understand the mechanism by which ltd regulates sleep behavior by taking 3 approaches: (1) I will analyze 4 ltd alleles for several aspects of sleep behavior, including overall sleep duration, sleep bout length, number of sleep bouts, latency to sleep, sleep rebound after deprivation, and total life span. (2) I will analyze the regulation of ltd using a quantitative PCR approach to determine if ltd is regulated by circadian drive, the homeostatic sleep drive, or light. (3) To determine in which brain regions ltd is sufficient to perform its sleep-regulation role, I will perform a tissue-specific rescue experiment with several GAL4 drivers that drive expression in known sleep-regulating areas of brain. The work proposed here will provide a better understanding of how the new sleep gene, ltd, regulates sleep. Furthermore, based on its connections to the molecular clock, learning &memory, and PKA, the proposed investigation of ltd could provide a molecular link between these disparate aspects of sleep biology. Finally, this work will identify ltd as an excellent candidate to aid in the diagnosis of sleep disorders such as insomina and somnabalism, as well as a potential drug target to offer treatment. We are interested in the function and regulation of sleep. Currently, we use the fruitfly, an animal that has recently been shown to be an excellent model for sleep behavior, to help understand how neural circuits control sleep/wake behavior, as well as to identify new genes that could be used to identify and treat sleep disorders in humans.